1. Field of Invention
This present invention relates generally to an automotive differential mechanisms and, more particularly, to lubrication of the gear meshes located in the differential housing.
2. Description of the Prior Art
A differential mechanism transmits rotary power differentially to output shafts from a ring gear driven by an external power source, such as an internal combustion engine or electric motor. A housing, formed of metal and secured to the ring gear, defines a chamber containing bevel pinions driveably connected to the housing by a spindle, a right-side bevel gear and a left-side bevel gear in continuous meshing engagement with the bevel pinions. The side bevel gears are driveably connected to a right-side output shaft and left-side output shaft, each shaft being driveably connected to a wheel of the vehicle.
The ring gear rotates through a fluid sump containing hydraulic lubricant, such as gear lube or automatic transmission fluid (ATF). As the ring gear and other components of the differential apparatus rotate, the ATF is carried from the sump on the surfaces of the ring gear teeth, and is slung onto the outer surface of the housing, from which it migrates into the housing sump. The ATF lubricates the bevel gears and side gears located in the chamber.
Ring gear churning through the sump oil produces in parasitic losses that degrade fuel economy. The level of lubricant in the sump is in part determined by the need to have the gear mesh wet at start-up to prevent damage due to high torque events before the meshing components are lubricated.
Alternatives to this approach include using baffles and pumps in the differential housing. Baffles have limited effectiveness across all operating conditions due to the need to maintain adequate oil flow to the pinion bearings and the axle does not typically uses pressurized oil flow to lubricate bearings. A pump adds significant cost and degrades fuel economy because it must draw a large amount of electric energy from the vehicle in order to pump cold, viscous gear oil.